Field of the Invention
The present invention relates to an organic light-emitting diode (OLED) display device that displays images.
Description of Related Art
Organic light-emitting diode (OLED) display devices have recently been prominent as next generation display devices. Such OLED display devices have some advantages, such as relatively fast response speeds, high contrast ratios, high light emitting efficiency, high luminance levels, and wide viewing angles, since OLEDs able to emit light by themselves are used therein.
Such an OLED display device includes subpixels arranged in the shape of a matrix, each of the subpixels including an OLED, and controls the brightness of selected pixels based on scanning signals. Each of the subpixels of the OLED display device also includes a driving circuit driving the OLED. The OLED driving circuit in each of the subpixels includes a transistor, a storage capacitor, and the like. The transistor of the driving circuit has unique characteristics, such as a threshold voltage, mobility, and the like.
The transistor of the driving circuit (in particular, a driving transistor supplying a current to an OLED) degrades along with the lapse of driving period, whereby the characteristics thereof may change. Thus, the characteristics of one driving transistor may have a difference from those of another driving transistor. Such differences in the characteristics between the driving transistors may be a main reason why subpixels have differences in the degrees of luminance, thereby degrading image quality. Therefore, functions able to sense and compensate for the characteristics of the transistors within individual subpixels have been developed.
In order to sense and compensate for the unique characteristics of a transistor within each of the subpixels, such as a threshold voltage, a saturated voltage of a specific sensing node is sensed (measured) by initializing a specific sensing node of the subpixel to a specific voltage value and subsequently changing the voltage value, and the characteristics of the transistor, such as the threshold voltage, are compensated based on the sensed voltage.
However, this approach of compensating the unique characteristics of a transistor, such as a threshold voltage, does not reflect changes in the unique characteristics of the transistor, such as the threshold voltage. In addition, this approach fails to completely compensate for the unique characteristics, such as the threshold voltage, since a sensor and a compensation circuit of an OLED display device have different resolutions. Consequently, stains may occur on the screen having low-grayscale luminance.